Hydrolytic resistance of model poly(ether urethane ureas) and poly(ester urethane ureas

ABSTRACT: Poly(ester urethane ureas) (PesURUs) and poly(ether urethane ureas) (Pe-tURUs) synthesized from diphenylmethane-4,49-diisocyanate and poly(butylene adi-pate) diol, and poly(tetramethylene oxide) diol or poly(propylene oxide) diol, respec-tively, were hydrolyzed at 70°C for various periods up to 16 weeks. Differences in thermal and mechanical properties of as-received dry samples are correlated with the number and strength of hydrogen bonds formed between urea/urethane groups of hard segments and polyester or polyether groups of soft segments. Gel permeation chroma-tography measurements show that the molar mass of linear PesURUs markedly de-creases with the hydrolysis time, whereas that of linear PetURUs remains almost unaffected. PesURU crosslinked by polymeric isocyanate has lower crystallinity, but shows somewhat better resistance to hydrolysis than its linear counterpart because of its more stable three-dimensional molecular structure. Water uptake at 37°C, dynamic mechanical thermal analysis, and differential scanning calorimetry thermograms de-termined for redried hydrolyzed specimens concurrently show that advancing hydroly-sis accounts for decrease in the crystallinity (if any) of soft polyester segments, in the efficacy of hydrogen bonding and in crosslinking density. Experimental data indicate that hydrolytic resistance of PetURUs is primarily determined by (1) the hydrolytic stability of individual types of present groups, (2) steric hindrances affecting the access of water molecules to these groups, and (3) the hydrophilicity of backbones. © 1998 Joh